St. Louis (KSDK) - The U.S. Coast Guard says they are monitoring the commercial and recreational vessels waiting to pass through the Port of St. Louis in the upper Mississippi River near Granite City, Illinois.

The Army Corps of Engineers closed Lock and Dam 27 because of a damaged protection cell that has hindered safe passage through the locks.

There are 30 vessels held both and below the lock and dam while repairs are underway.

Lock and Dam 27 is at mile-marker 185 just above St. Louis, and is the busiest lock and dam on the Mississippi River. It moves over 73 million tons of cargo each year.